Protein tyrosine phosphatase reactions

Computational enzymology Protein tyrosine phosphatase reactions... 

Figure 4 Schematic diagram of the first step of the reaction catalyzed hy bovine protein tyrosine phosphatase (BPTP) formation of the cysteinyl phosophate intermediate.

Other electrophilic substitution reactions on aromatic and heteroaromatic systems are summarized in Scheme 6.143. Friedel-Crafts alkylation of N,N-dimethyl-aniline with squaric acid dichloride was accomplished by heating the two components in dichloromethane at 120 °C in the absence of a Lewis acid catalyst to provide a 23% yield of the 2-aryl-l-chlorocydobut-l-ene-3,4-dione product (Scheme 6.143 a) [281]. Hydrolysis of the monochloride provided a 2-aryl-l-hydroxycyclobut-l-ene-3,4-dione, an inhibitor of protein tyrosine phosphatases [281], Formylation of 4-chloro-3-nitrophenol with hexamethylenetetramine and trifluoroacetic acid (TFA) at 115 °C for 5 h furnished the corresponding benzaldehyde in 43% yield, which was further manipulated into a benzofuran derivative (Scheme 6.143b) [282]. 4-Chloro-5-bromo-pyrazolopyrimidine is an important intermediate in the synthesis of pyrazolopyrimi-dine derivatives showing activity against multiple kinase subfamilies (see also Scheme 6.20) and can be rapidly prepared from 4-chloropyrazolopyrimidine and N-bromosuccinimide (NBS) by microwave irradiation in acetonitrile (Scheme... 

The synthesis of benzo[Z>]furan derivatives has become a very active field because these molecules have been recently identified as having a variety of biological activities. For example, they can function as inhibitors of protein tyrosine phosphatase IB with antihyperglycemic properties <00JMC1293>, as well as potent and short-acting p-blockers in the treatment of various cardiovascular diseases . An inexpensive, reusable clay has been utilized to catalyze a facile cyclodehydration under microwave without solvent to form 3-substituted benzo[2>]furans from substituted a-phenoxy acetophenones 104. One of the important features of this procedure is that all the selected cyclodehydration reactions are complete in less than 10 minutes <00SL1273>. 

The piperazine-substituted pyrimido[5,4-< ][l,2,4]triazine 103 undergoes selective reaction with benzylic halides to provide the benzylic piperazinyl analogues 104 <2003BML2895> as shown in Equation (15). The products are protein tyrosine phosphatase inhibitors. 

Fig. 5.5. General functions of transmembrane receptors. Extracellular signals convert the transmembrane receptor from the inactive form R to the active form R. The activated receptor transmits the signal to effector proteins next in the reaction sequence. Important effector reactions are the activation of heterotrimeric G-proteins, of protein tyrosine kinases and of protein tyrosine phosphatases. The tyrosine kinases and tyrosine phosphatases may be an intrinsic part of the receptor or they may be associated with the receptor. The activated receptor may also include adaptor proteins in the signaling pathway or it may induce opening of ion channels.

The TS for the tyrosine phosphate hydrolysis by the enzyme protein tyrosine phosphatase (PTP1B) has been determined using a hybrid QM(PM3)/MM potential.271 The reaction was found to be dissociative in character with no P—S bond formation in the TS but extensive P—O bond lengthening. 

Studies of the oxidation of organic sulfides with amino acid-derived ligands in acetonitrile revealed very little difference between the mechanism of their oxidation and that of halides, except for one major exception. Despite the fact that acid conditions are still required for the catalytic cycle, hydroxide or an equivalent is not produced in the catalytic cycle, so no proton is consumed [48], As a consequence, there is no requirement for maintenance of acid levels during a catalyzed reaction. Peroxo complexes of vanadium are well known to be potent insulin-mimetic compounds [49,50], Their efficacy arises, at least in part, from an oxidative mechanism that enhances insulin receptor activity, and possibly the activity of other protein tyrosine kinases activity [51]. With peroxovanadates, this is an irreversible function. Apparently, there is no direct effect on the function of the kinase, but rather there is inhibition of protein tyrosine phosphatase activity. The phosphatase regulates kinase activity by dephosphorylating the kinase. Oxidation of an active site thiol in the phosphatase prevents this down-regulation of kinase activity. Presumably, this sulfide oxidation proceeds by the process outlined above. 

Nxumalo, F. and A.S. Tracey. 1998. Reactions of vanadium(V) complexes of N,N-dimethylhydroxylamine with sulfur-containing ligands Implications for protein tyrosine phosphatase inhibition. J. Biol. Inorg. Chem. 3 527-533. 

Reversible chemical modification of enzymes, which was discovered in 1955 by Edmond Fischer and Edwin Krebs [58], is a more prevalent mechanism for cellular signaling switching. Fischer and Krebs showed that enzymes can be turned from an inactive form to an active form via phosphorylation of certain residues of the protein. Enzymes that catalyze phosphorylation (addition of a phosphate group coupled with ATP or GTP hydrolysis) are called protein kinases. Enzymes that catalyze dephosphorylation (which is not the reverse reaction of the phosphorylation) are called phosphatases. For example, a protein tyrosine phosphatase is an enzyme that catalyzes the removal of a phosphate group from a tyrosine residue in a phosphorylated protein [57],... 

Mechanistically, inhibition must not necessarily block the active site itself, but it can exert allosteric effects on the substrate-binding pocket, which thereby enhances or suppresses enzymatic activity. Additional considerations regarding enzymatic reactions are discussed in Reference 86. SAR by NMR has been successfully applied to various systems [i.e., for disrupting intracellular protein-protein binding (87) as well as cytokine-receptor interaction (88)]. High-affinity enzyme inhibitors have been developed by this technique [e.g., for the metalloproteinase Stromelysin (89) and the protein tyrosine phosphatase IB (90)]. 

Figure 2. The reaction catalyzed by the protein tyrosine phosphatases.

Zhao Y, Wu L, Noh SJ et al (1998) Altering the nucleophile specificity of a protein-tyrosine phosphatase-catalyzed reaction. Probing the function of the invariant glutamine residues. J Biol Chem 273 5484-5492... 

Hydrolysis of the phospho-Cys intermediate that forms during reactions of protein-tyrosine phosphatase is accompanied by a solvent isotope effect of 1.5 [47,... 

The phospho-Cys intermediate that forms during the course of reactions catalyzed by protein-tyrosine phosphatase is stabilized by hydrogen-bond donation from backbone residues of the so-called P-loop comprising Cys , Arg , and Thr as well as the guanidinium moiety of Arg [49]. These interactions also serve to stabilize the Michaelis complex. 

MALDI-TOF-MS has been demonstrated as a useful tool in pre-steady state kinetic research by Houston et al., who combined it off-line with quench-flow methods to follow the appearance of a protein tyrosine phosphatase (PTPase) reaction intermediate.12 Houston et al. were able to measure rate constants up to 30 s 1, with k2/k3 ratios up to approximately 15. The device described in this chapter extends this technique to measure rate constants approximately 5 times greater, with k2/k3 ratios approximately twice previously measurable values. MALDI-TOF-MS is typically conducted on a centimeter-scale conducting plate the digital microfluidic system employed is a square plate approximately 2 cm on each side, with 16 experimental units per chip, which can be placed directly inside a standard MALDI-TOF-MS plate that has been machined appropriately. By grounding the exposed wires on the otherwise insulated chip, charging is negligible. 

This would be analogous to the change that results from alkyl substitution that is, transition states become more associative in the continuum from monoesters to triesters. Although relatively few phosphatases have been subjected to serious scrutiny of their transition states, in the cases that have been reported, this prediction has not been borne out. The reactions catalyzed by AP proceeds through loose transition states that are not significantly altered from those in solution, both in its phosphatase and in its promiscuous sulfatase activities. " Results with A-phosphatase and with calcineurin, which both catalyze phosphoryl transfer to a metal-coordinated hydroxide nucleophile, also provide no evidence of a significantly different transition state. Protein tyrosine phosphatases (PTPs), which do not contain metal ion cofactors but have a conserved arginine residue and proceed via a phosphocysteine intermediate, similarly catalyze phosphoryl transfer via a transition state similar to the one in solution. ... 

The reactivity of the Ru-pac complexes toward the binding of the above thio-amino acids (RSH) has been reportedly used to explore the potential role of Ru-pac complexes in the inhibition of the activity of cysteine protease (CP) (25,26) and protein tyrosine phosphatase (PTP) (28). The Ru-pac complexes were found to inhibit protease activity of the three enzymes bromalien, papain, and ficin, while azo-albumine was used as the substrate (25,26). The ability of Ru-pac complexes to inhibit CP activity was attributed to the high affinity of the ruthenium complexes toward binding the SH group in the cysteine residue of the enzymes via a rapid aqua-substitution reaction (Scheme 8). 

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